Electronic cooking appliance

ABSTRACT

A magnetron is coupled to a wave guide having an open end exciting a transition section which is spproximatelytwo wavelengths square. The transition section approximately two box is secured over the microwave cavity which has a circular opening formed in the top wall thereof. A disk having a plurality of apertures or slots is rotatably supported beneath the upper cavity wall in close proximity thereto so that energy is radiated into the cavity in such a manner as to produce uniform and linear heating throughout the cavity. The apertures in the disk appear electrically at multiples of substantially half-wavelengths from the point of the magnetron coupling when the longder dimension of the apertures are transverse to the longitudinal dimension of the wave guide.

United States Patent [191 Whiteley 3,746,823 [4 1 July 17, 1973 ELECTRONIC COOKING APPLIANCE Lloyd L. Whiteley, 15520 Wing Lake Dr., Minnetonka, Minn. 55343 22 Filed: Feb. 28, 1972 21 Appl. No.: 229,790

[76] Inventor:

[52] US. Cl. 2l9/l0.55 [51] Int. Cl. .2 H05b 9/06 [58] Field of Search 219/10.55

[56] References Cited UNITED STATES PATENTS 2,920,174 1/1960 Haagensen 219/1055 2909.635 10/1959 Haagensen 219/1055 3,641,301 2/1972 lkeda 219/1055 Primary ExaminerJ. V. Truhe Assistant Examinerl-lugh D. Jaeger Attorney-Everett J. Schroeder et al.

I [57] ABSTRACT A magnetron is coupled to a wave guide having an open end exciting a transition section which is spproximatelytwo wavelengths square. The transition section approximately two box is secured over the microwave cavity which has a circular opening formed in the top wall thereof. A disk having a plurality of apertures or slots is rotatably supported beneath the upper cavity wall in close proximity thereto so that energy is radiated into the cavity in such a manner as to produce uniform and linear heating throughout the cavity The apertures in the disk appear electrically at multiples of substantially half-wavelengths from the point of the magnetron coupling when the longder dimension of the apertures are transverse to the longitudinal dimension of the wave guide.

17 Claims, 6 Drawing Figures Pat exited July; 17, 1973 3 Sheets-Sheet 1 .FIG, 2.

ELECTRONIC COOKING APPLIANCE BACKGROUND OF INVENTION Microwave cooking or heating devices have been in existence for some time incorporating standing waves of high frequency energy which are directed into the oven cavity and reflected within the cavity to accomplish the heating or cooking process. Due to the nature of the standing waves, there are localized areas of high electric field intensity and localized areas of low electric field intensity within the oven cavity. Distribution of the microwave energy in this manner obviously results in relatively hot or cold spots within the cavity and generally speaking with a large area to be covered, such as in the baking process, unless the cold and hot spots are eliminated, the process using microwave energy does not perform the baking process in an acceptable manner. In fact, the true test of a microwave oven is to determine if it will bake rather than merely produce calized heating which may be acceptable in certain foods such as meats or smaller food items such as baked potatoes, cupcakes, and the thawing of certain small frozen foods.

Different approaches have been taken to solve the problem of production of :hot and cold spots ranging from attempts to change the pattern of the standing waves by electronically varying the frequency of oscillation of the magnetron used to excite the cavity, and thus produce standing wave patterns of different wavelengths, to attempts which make use of certain mechanical mode stirrers for theoretically causing a change in the geometric space of the microwave cavity. While it proves to be rather impractical to change walls of the microwave cavity, the walls may be electrically deformed or changed through the use of certain devices such as a mode stirrer assembly which simulates the effects of deforming or moving the walls. One such approach is disclosed in U. S. Pat. No. 3,521,019 in which a number of vanes are positioned adjacent to one of the walls of the cavity so that the spacing between the vanes which are oriented like a venetian blind is not greater than one-quarter wavelength of the microwave energy and the distance between the vanes and adjacent wall when closest to the wall is no greater than one-quarter wavelength. The inventormaking use of the venetian wave guide technique also recognizes that the electronic mode of operation may also be changed by providing multiple inputs to the microwave cavity. It is further recognized that using more than one input to the cavity does require critical placement of the wave guides relative to the microwave cavity.

Another approach to changing the reflective configuration within the cavity has been through the use of bladed stirrers such as disclosed in U. S. Pat. Nos. 3,43l ,381', 3,281,567; 3,364,332; 3,505,491; and 3,517,152. Basically, all of these structures have one thing in common in that they attempt to change the standing wave patterns within the cavity by reflecting the standing waves towards the magnetron and thus change the standing wave patterns within the cavity to distribute the hot and cold spots. They also recognize that in using such a structure, the greater the area within the cavity that is affected by the blades, theoretically there should be a more even distribution of the microwave energy. For this reason, some of the disclosures are directed to the use of more than a single stirrer, and some use motors having various speeds to drive the stirrers so as to create random reflections and thus tend to avoid introducing secondary or auxiliary hot and cold spots. This technique is used even more extensively where the cavity may be thought of as including a double size or being energized by two different sources of microwave energy.

Other approaches are also taken where it is permissible to allow the food to be moved within the cavity and such an approach is disclosed in U. S. Pat. Nos. 3,478,188 and 3,474,212. ln each of these disclosures, the mode of operation is generally made at some mode other than the dominant mode, or TE m mode of operation. However, it must be recognized that each of these ovens is designed for a particular purpose and does permit a conveyor to move through the oven. It will also be noted that each of these ovens makes use of mechanical stirrers on as many as three different walls of the oven to increase the chances of creating reflective waves within the cavity. It will also be apparent from the disclosures set forth thus far, that the stirrers take on a multitude of different configurations.

Another slightly different approach in an oven utiliz' ing a conveyor, is found in U. S. Pat. No. 3,263,052 in which the oven or cavity is some eight feet long and uses a wave guide which is some 5 feet long to excite the oven. Slots are formed in the wave guide and various reflectors are used between the slots in the wave guide to improve the standing wave pattern within the cavity. However, it is obvious that it is impractical to employ an 8 foot long oven with a conveyor used therewith to attempt to create a condition which has uniform heating within the cavity.

Another approach to creating an even distribution of the energy within the cavity is found in U. S. Pat. No. 3,436,507 which utilizes a circular non-metallic material for supporting certain narrow metal strips, the entire structure being secured to a conical transition member extending from the end of a coaxial coupler, the combination being rotatable. The structure is apparently designed to again produce reflective waves within the cavity in such a manner that the standing wave p'attems are broken up. A similar approach is disclosed in U.'S. Pat. No. 3,471,671 in which the disk is driven by an air stream. 1

Several of the inventors whose disclosures have been made thus far have taken the position that a moving antenna distribution system is generally proven to be the least suitable for attempting to solve the problernof eliminating the hot and cold spots. I I

Other approaches solving the problem are set forth in U. S. Pat. Nos. 3,474,211 and 3,475,577 in which some form of reflective element is placed directly in the wave guide and is moved or rotated to change the standing wave patterns. The one approach is accomplished through the use of a parabolic shaped wave guide in which disks are used having radially extending slots to provide some form of reflective elements. In the latter disclosure, reflective elements are introduced along the longitudinal axis of the wave guide and is repeated at distances of half-wavelengths to produce different reflective waves towards the magnetron. One of the disclosures additionally introduces a rotating heating plane so that the food may be rotated within the cavity in an additional attempt to eliminate hot and cold spots. Movement of the food to be heated within the oven, both horizontally and vertically is similarly disclosed in U. S. Pat. No's 3,428,772 and 3,436,506.

U. S. Pat. No. 3,439,143 discloses a microwave oven having a mode stirrer which is located within the wave guide rather than in the microwave oven cavity. The inventor there suggests that changes within the wave guide have a much better chance of providing uniform distribution of energy within the cavity because the socalled paddle wheel stirrers have a limited effect in providing uniformity of heating. The disclosure in the latter reference is directed to placing a rotatable element within the wave guide between two openings into the cavity such that when a reflective strip is placed upon the rotatable element, it will alternately act like a gate in producing an open condition and a shorted condition thus permitting energy to be alternately ap plied through the two openings and thus create a means of changing the standing wave patterns within the cavity.

Another means of introducing energy in a uniform distribution within a cavity is disclosed in U. S. Pat. No. 3,493,709 which is directed to a form of spiral antenna. The inventor there also notes that in attempting to use a resonant disk antenna having a diameter which is ap' proximately one-half wavelength and disposed near the upper wall of the oven, the food would cook at a higher rate around'the periphery of the cavity than in the center thereof. The inventor considered such an approach to be undsirable.

SUMMARY OF THE INVENTION This invention relates to the field of electronic cooking appliances and more particularly to a means of controlling the microwave radiation between the wave guide and a heating or cooking cavity.

The present invention recognized the deficiencies which have been prevalent in the art and from the background of the invention, it should also be apparent that the problems which various inventors have attempted to solve still remain. The instant invention makes use of a magnetron which energized the wave guide in the dominant mode or the TE mode of operation. The wave guide is connected to a transition wave guide or box along one of the side walls with the longitudinal axis of the wave guide intersecting the center point of the transition box Generally speaking, the transition section is approximately two wavelengths square. For the preferred embodiment of the invention, the frequency of operation of the magnetron is at 2450 X Hz having a wavelength of approximately 4.81 inches. A tuning stub is also used at an appropriate point in the transition section to tune the wave guide in such a manner that various loadings of the cavity will not affect the mode of operation of the magnetron.

The heating cavity is located directly below the transition box and is coupled to the transition box through an opening which is circular in nature, the upper wall of the cavity and lower wall of the wall guide transition section being common to each other. A disk is rotatably secured in close proximity to the lower surface of the wall just described having the opening formed be tween the transition wave guide section or box and the cavity so that it may be considered that the disk and common wall are coplanar. This disk is supported for rotation through the use of a non-metallic shaft which is supported above through the upper edge or wall of the transition wave guide section or box, the upper portion of the shaft being driven by a low speed motor which generally operates between approximately 13 to l8 revolutions per minute. Because it is generally known that maximum coupling is obtained from a magnetron to a wave guide in the dominant mode by coupling at quarter-wavelength point, maximum transfer of energy down the wave guide would then occur at multiples of half-wavelengths from that point. The disk is secured within the transition box along the longitudinal axis of the wave guide at a point representative of ap proximately two wavelengths. The disk has a number of apertures formed therein which are elongated and sequentially oriented transverse to the longitudinal axis of the wave guide at multiples of half-wavelengths. That is, regardless of whether the aperture is nearest the magnetron or rotated to a position which is furthest from the magnetron, when the apertures are transverse to the longitudinal axis of the wave guide, they appear electrically at multiples of half-wave points from the magnetron, and thus would appear to produce a radiation system permitting maximum power transfer to the cavity. With this type of system, there is no reflection of the waves within the cavity back to the magnetron or within the wave guide. Therefore, it would appear that the operation of the disk is independent of the size of the cavity. The load seen by the magnetron may be varied or modified by the position of the resonant stub and the disk is prevented from arcing with respect to the wall of the cavity or wave guide transition section through the use of a plurality of insulated spacers which prohibit the disk and the other surface from rubbing together.

In keeping with the teachings of the present invention, it is a general object to provide an electronic cooking appliance which receives its energy through a rotating disk having at least one elongated aperture.

It is another object of this invention to provide an electronic cooking appliance with a cavity having substantially uniform and linear heating characteristics.

It is still another object of the present invention to provide a means of energizing an electronic cooking appliance by a rotating disk having apertures substantially coplanar with a wall of the cavity.

It is yet another object of this invention to provide a means of energizing an electronic ooking appliance by a rotating disk having apertures substantially coplanar with a wall of the larger dimension of the wave guide.

It is a further object of the invention to provide a means ofenergizing an electronic cooking appliance by a rotating disk having a plurality of elongated apertures, rotatable to appear at multiples of substantially half-wavelengths from the point of energizing the wave guide.

It is a still further object of this invention to provide a means of energizing an electronic cooking appliance by a rotating disk having a plurality of elongated apertures where the apertures are constructed and arranged in the disk so that the longitudinal axes thereof are in non-parallel alignment and the angles between the same are substantially less than normal to each other.

It is still a further object of this invention to provide a means of energizing an electronic cooking appliance by a rotating disk having a plurality of elongated apertures where the apertures are constructed and arranged so that they appear sequentially at multiples of substantially half-wavelengths from the coupling means.

It is still another object of this invention to provide a means of energizing an electronic cooking appliance by a rotating disk having a plurality of apertures where the disk forms a part of a transition wave guide substantially two wavelengths square and has its center concentric with that of the disk and appearing substantially two wavelengths from the point of energizing the wave guide.

These and other objects and advantages of the invention will more fully appear from the following description made in connection with the accompanying drawings, wherein like reference characters refer to the same or similar parts throughout the several views and in which:

FIG. 1 is a perspective view of the front of an electronic cooking appliance incorporating the invention;

FIG. 2 is a back perspective view of the electronic cooking appliance with the outer cover removed;

FIG. 3 is a top plan view of the electronic cooking appliance with the cover removed exposing the transition section or feedbox and a portion of the disk;

FIG. 4 is a side elevation view of the electronic cooking appliance with the cover off as seen looking into the end of the wave guide;

FIG. 5 is a top plan view of the disk showing all of the details of the placement and size of the apertures formed therein; and

FIG. 6 is a diagram showing the relationship of the standing wave patterns in the wave guide and transition box.

FIG. 1 discloses a microwave oven 10 which has a front panel to which is secured a door 12. The oven has acabinet cover 13 which covers the rear portion of the oven. Several oven controls 14 and 15 are also secured to the front panel 11.

FIG. 2 discloses the rear of microwave oven 10 where a magnetron 16 is coupled to a wave guide 17 in the normal manner for a TE mode of operation and further includes a shroud or housing 18 which is used to cool magnetron 16 through the use of a blower 20. A power supply 21 is secured to the base plate of the oven and a junction box 22 is secured to the back of the base plate. An oven cavity 23 is secured in the center of the microwave oven and secured to the upper portion of the cavity is a microwave transition section or box 24. A motor 25 is secured to the upper portion of cavity 23 or the edge of transition section 24 to drive a pulley 26 through the use of a belt 27. A tuning stub 28 is also secured in the upper edge of transition section 24, to insure that a proper standing wave ratio is obtained and that the magnetron 16 operates in the proper mode. A wave guide adaptor 30 also helps secure wave guide assembly 17 to transition section 24. i

As shown in greater detail in FIGS. 3 and 4, wave guide 18 is secured to the transition box 24 through suitable means such as bolts 31 which are secured through a side wall of box 24 and wave guide adaptor 30, bolts 31 being connected to a pair of brackets 32 and 33 which are secured to wave guide 18. Wave guide 18 is connected in open-end fashion through an opening 34 formed in a side wall of transition box 24. Wave guide 18 may include a transition section between wave guide adaptor 30 and a coupling point 35 which is located axially with the center hole ofa plurality of circular spaced ventilating holes 36. For the embodiment disclosed, magnetron 16 has an operating frequency of 2,450 X 10 Hz and the wave guide has a height of 2.25 inches where coupled to the magnetron and is reduced to a height of l inch where coupled to transition box 24. The wave guide width is maintained at 3.75 inches. It will also be generally understood that the magnetron is coupled to the wave guide at a multiple of a guarter-wavelength from the closed end of the wave guide. The distance from the point of coupling to the wave guide from the magnetron to the end secured to transition box 24 is 5.002 inches.

Pulley 26 is coupled to a shaft 40 which is formed of a non-metallic material such as polypropylene. A bushing 41 forms a journal for shaft 40 and is secured in the center at the top of the transition box 24. Shaft 40 extends downwardly and is connected to a hub 42 which is secured to a disk 43. The distance from coupling point 35 to the position of the axis of shaft 40 along a longitudinal axis of wave guide 18 is approximately two wavelengths.

A plate 45 forms the upper wall of cavity 23 and has a central circular opening 46 formed therein. It is through this opening that shaft 40 extends to secure disk 43 at a position slightly below that of wall 45. A plurality of insulated spacers 47 are secured between the bottom surface of plate 45 and disk 43, the spacers being approximately one-sixteenth inch in thickness and are disposed between the two surfaces to prevent arcing in the cavity. For all practical purposes, plate 45 and disk 43 may be considered to be substantially coplanar. Opening 46 has a smaller diameter than the diameter of disk 43. In the instant application, the cavity is 14 inches square and the sides of the transition. box 24 which are normal to wave guide 18 are 9.44 inches long and the sides which are parallel to the longitudinal axis of wave guide 18 are 9.12 inches long, the opening 46 in plate 45 being 8 inches in diameter. The distance from the top of the transition box to its base is 2.250 inches, the wave guide opening being 0.498 inches below the upper surface of the transition box 24. A circular ring 48 is depressed in the top of transition box 24 having an outer radius of 2.375 inches and an inner radius of 1.60 inches, the central portion being depressed 0.38 inches, and a sloping portion 49 between the two radii joining the top with a curvature of 0.50 inch radius.

Disk 43 is shown in more detail in FIG. 5 wherein eight holes 50 are equally spaced around the rim of the disk at a diameter of 9 inches, the disk being formed of a metallic material such as aluminum and having a diameter of IO inches. Holes 50 are formed in disk 43 to accomodate the spacers 47 which are generally formed with a flange so that they may be pressed into holes 50 and held in place. Disk 43 contains threeelongated apertures 51 through 53 having a length of 2.31 inches and a fourth elongated aperture 54 having a length of 1.920 inches, all of the apertures being 0.250 inches wide. A pair of center lines 55 and 56 are representative of axes which are longitudinally and transversely oriented respectively with respect to the longitudinal axis of wave guide 18. Thus it will be seen that when aperture 51 is oriented in the position shown in FIG. 5, and as found in FIG. 3, the midpoint of the aperture is approximately 1.92 wavelengths from the magnetron coupling 35. When aperture 51 is rotated l it will appear adjacent to transverse axis 56'and will be approximately 2.05 wavelengths from coupling point 35.

With the disk rotating counterclockwise as seen in FIGS. 3 and 5, aperture 52 would have been transverse to axis 55 just prior to the appearance of aperture 51 and in this position, aperture 52 is 1.50 wavelengths from the magnetron coupling point 35. Upon aperture 52 being oriented transverse to longitudinal axis 55 at a point 180 degrees from that shown in FIG. 5, aperture 52 will be approximately 2.47 wavelengths from coupling point 35.

Aperture 53 will appear electronically at a transverse position relative to axis 55 prior to apertures 52 and 51 and in so doing, will be oriented approximately l.95 wavelengths from magnetron coupling point 35 and when rotated 180 from such position, will then appear transverse to longitudinal axis 55 at approximately 2.02 wavelengths.

Aperture 54 when appearing closest to coupling point 35 and transverse to axis 55, appears at a position of 1.52 wavelengths from magnetron coupling 35 and when rotated 180 appears at a position of 2.46 wavelengths from magnetron coupling point 35.

The results just described are shown diagrammatically in FIG. 6 where it will be observed that each of the transverse appearances of the apertures 51, 52, 53, and 54 with respect to the magnetron coupling point 35 is at a multiple ofa half-wavelength and thus maximum transfer of the energy through the apertures is achieved. In fact, when apertures 51 through'54 are aligned with their longitudinal axes parallel to the longitudinal axis 55, a minimum amount of energy will be transferred into cavity 23. With the microwave energy radiating through apertures 51 54, it will be observed that there is virtually no reflection from cavity 23 back towards the magnetron such as may be experienced when exciting a cavity with an open-ended or large aperture or iris formed in a wave guide. Additionally, cavity 23 then becomes substantially independent of the frequency for a particular area within the cavity. It will be observed that FIG. 4 additionally discloses a front opening 60 which is closed through appropriate electrical sealing means by door 12 and a cooking or heating plane or shelf 61 is formed above a bottom member 62 of cavity 23. Adequate ventilation vents 63 may be formed in cavity 23 by the appropriate forming of small holes in the side walls to allow the escape of cooking vapors without permitting microwave energy to escape therethrough. In the instant application, the cooking cavity is 8.875 inches high with the shelf 61 being elevated 1.50 inches above floor 62, which means that the distance from disk 43 to shelf 61 is also a multiple of substantially half-wavelengths. In the present invention the distance is approximately one and one-half wavelengths.

It has also been found that the same principles enumerated herein are equally applicable to ovens which are generally thought to be of double" cavity size, that is, where two different magnetrons are used to feed the oven cavity. Again, the oven cavity width and length may be varied without regard to the general requirements of attempting to maintain some relationship to the operating frequency or wavelength. Through the use of the apertured disk 43 the radiation is directed into cavity 23 much like a sprinkler in which the sprinkler head is rotated so as to bathe everything within the cavity, In fact, tests have been made in which at least 16 containers were placed in the oven in a square pattern, each of the containers being formed of styrofoam and containing eight ounces of water. The temperature of the water was measured initially in each of the containers and after the oven was excited for 1% minutes, the results indicated that after two tests, the difference between the highest and the lowest temperature was 29 F. A similar test was run on a microwave oven embodying the state of the art at present using a cavity with a stirrer and after both tests had been completed, the difference between the highest and the lowest temperature was 21 F for the first test and 22 F for the second test. It was also observed that there was more usable energy in the instant invention than that embodying the present state of the art, and that the in stant invention produced power which was very close to the rated power rating whereas the oven embodying the present state of the art was considerably lower than the rated power.

Other tests involving the use of the 16 containers has provided additional-proof of the principles of operation of the oven. With aperture 53 aligned transverse to axis 55, readings were taken of the total temperature rise of the water after 1% minutes of energization, the total being l28 C and this would be proportional to the radiation entering the cavity. Aperture 53 was then rotated until it was nearest wave guide 18 and substantially parallel to axis 55. In this position, the 16 containers (containing 8 ounces of water each) were again subjected to 1% minutes of radiation, and the total temperature rise was found to be 84.5 C. However, upon moving disk 43 counterclockwise to a position representative of approximately 6 to 18 beyond the position of longitudinal axis 55, the magnetron received reflected waves of such magnitude that different moding occurred and the amount of radiation passing through slots 51 through 54 would have to be considered at a minimum.

An additional test was developed in which 16 containers were placed in the oven in a square pattern in the same manner as indicated previously, each contain ing 8 ounces of water, and disk 43 was rotated in the normal manner in a counterclockwise direction at a speed of approximately 13 rpm, for 1% minutes. The total temperature rise was then recorded as 111 degrees C. What is more important however, is that the uniformity stated above was maintained.

To further compare the prior art to that of the instant invention, sheets of Thermofax paper were inserted in the ovens with a black backing material being held in close proximity thereto through the use of a clear plastic holder having sheets of the material both above and below the Thermofax paper. As a result of energizing the two different ovens, it was found that the oven em ploying the present state of the art produced a hot spot so intense that a hole approximately 1% inches in diameter was burned through the upper sheet of the plastic material, the Thermofax paper, and the material was burned through on the back side thereof. Additionally, there were four other hot spots shown on the paper, all of which occurred at the end of 45 seconds.

The same test was made of the instant invention and after 3 minutes of operation, there were no burned spots on the plastic material, or the Thermofax paper, and there was a more even distribution of energy indicated from the pattern established on the Thermofax paper.

From the results of the test just described, it should be apparent that the maximum transfer of energy is occurring through the apertures in the disk at a position where the apertures are transverse to the longitudinal axis of the wave guide and a minimum amount of en ergy is transferred to the cavity when the apertures are aligned substantially parallel to the longitudinal axis of the wave guide. Thus the description of the principles of operation as disclosed in FIG. 6 are shown to be correct.

It will of course, be understood that various changes may be made in the form, details, arrangement and proportions of the parts without departing from the scope of the invention which consists of the matter shown and described herein and set forth in the appended claims.

What is claimed is:

1. An electronic cooking appliance comprising:

a. a microwave generator including coupling means for coupling microwave energy into a wave guide;

b. a microwave cavity constructed and arranged to receive objects to be heated and having a central opening formed in one wall thereof;

c. a wave guide transition box disposed over said central opening in said cavity, said box and said cavity having walls forming a barrier to the transmission of microwave energy except through said central opening, said box having a wave guide opening formed in one wall thereof;

d. a wave guide operably connected between said microwave generator and the wave guide opening in said wave guide transition box for conducting microwave energy therebetween;

e. a disk rotatably supported about an axis substantially coaxial with said central opening and having a periphery extending outwardly at least to the periphery of said central opening in a plane substantially coplanar with the wall containing said central opening, said disk having at least one aperture therein distributing said microwave energy between said transition box and said cavity;

f. and motor means operably connected to said disk for rotation thereof.

2. The structure set forth in claim 1 including:

g. insulated spacers secured around the periphery of said disk and disposed between said disk and said wall of said cavity, said spacers eliminating arcing between said disk and said cavity wall.

3. The structure set forth in claim 1 wherein said central opening is circular having its center a plurality of substantially half-wavelengths from said coupling means, said disk having a greater diameter than said central opening.

4. The structure set forth in claim 1 wherein at least said one aperture has an elongated shape of which the longer dimension, when transverse to the longitudinal dimension of said wave guide appears at multiples of substantially half-wavelengths from said coupling means.

5. The structure set forth in claim 3 wherein said transition box is substantially two wavelengths square and has its center concentric with said central opening.

6. The structure set forth in claim I wherein said motor means drives said disk at a speed less than 100 rpm.

7. The structure set forth in claim 1 including:

h. a tuning element aligned parallel to said axis of rotation for said disk and disposed in a wall opposite that having said disk adjacent thereto and disposed to produce low microwave power variations for different loads placed in said microwave cavity.

8. An electronic cooking appliance comprising:

a. a microwave generator including coupling means for coupling microwave energy into a wave guide;

b. a microwave cavity constructed and arranged to receive objects to be heated and having a central opening formed in one wall thereof;

c. a wave guide transition box disposed over said central opening in said cavity, said box and said cavity having walls forming a barrier to the transmission of microwave energy through said central opening, said box having a wave guide opening formed in one wall thereof;

d. a wave guide operably connected between said microwave generator and the wave guide opening in said wave guide transition box for conducting microwave energy therebetween;

e. a disk rotatably supported about an axis substantially coaxial with said central opening and having a periphery extending outwardly at least to the periphery of said central opening, said disk extending in a plane substantially coplanar with the wall containing said central opening, said disk having a plurality of apertures formed therein with elongated shapes of substantially parallel sides, of which the longer dimension when transverse to the longitudinal dimension of said wave guide appears at multiples of substantially half-wavelengths from said coupling means for distributing said microwave energy between said transition box and said cavity;

f. and motor means operably connected to said disk for rotation thereof.

9. The structure set forth in claim 8 wherein said plurality of apertures have at least two apertures of equal dimensions and at least one aperture of other dimensions.

10. The structure set forth in claim 8 wherein each of said plurality of apertures has a ratio of length to width of approximately 7.68 to 9.25.

11. The structure set forth in claim 8 wherein said plurality of apertures are constructed and arranged in said disk so that the longitudinal axes thereof are in non-parallel alignment and the angles between the same are substantially less than normal to each other.

12. The structure set forth in claim 11 wherein said plurality of apertures are constructed and arranged so that they appear sequentially at multiples of substantially half-wavelengths from said coupling means.

13. The structure set forth in claim 8 wherein said wave guide has an open end operably connected to the wave guide opening in said wave guide transition box, said wave guide opening extending through a wall substantially parallel to said disk rotational axis.

14. The structure set forth in claim 8 wherein said disk used with a microwave generator having a frequency of 2450 X 10 Hz has apertures specifically constructed and arranged as shown in FIG. 5 hereof.

15. The structure set forth in claim 8 wherein said plurality of apertures are disposed in said disk so that the part of said aperture farthest from the center of said disk is less than a wave guide width when transverse to the longitudinal axis of said wave guide.

16. The structure set forth in claim 1 including:

i. a shelf defining a cooking plane disposed below said disk at a distance representative of substan tially a multiple of half-wavelengths.

17. The structure set forth in claim 8 wherein said wave guide transition box includes an indented ring portion extending downwardly from the top of said box in a smooth curve. 

1. An electronic cooking appliance comprising: a. a microwave generator including coupling means for coupling microwave energy into a wave guide; b. a microwave cavity constructed and arranged to receive objects to be heated and having a central opening formed in one wall thereof; c. a wave guide transition box disposed over said central opening in said cavity, said box and said cavity having walls forming a barrier to the transmission of microwave energy except through said central opening, said box having a wave guide opening formed in one wall thereof; d. a wave guide operably connected between said microwave generator and the wave guide opening in said wave guide transition box for conducting microwave energy therebetween; e. a disk rotatably supported about an axis substantially coaxial with said central opening and having a periphery extending outwardly at least to the periphery of said central opening in a plane substantially coplanar with the wall containing said central opening, said disk having at least one aperture therein distributing said microwave energy between said transition box and said cavity; f. and motor means operably connected to said disk for rotation thereof.
 2. The structure set forth in claim 1 including: g. insulated spacers secured around the periphery of said disk and disposed between said disk and said wall of said cavity, said spacers eliminating arcing between said disk and said cavity wall.
 3. The structure set forth in claim 1 wherein said central opening is circular having its center a plurality of substantially half-wavelengths from said coupling means, said disk having a greater diameter than said central opening.
 4. The structure set forth in claim 1 wherein at least said one aperture has an elongated shape of which the longer dimension, when transverse to the longitudinal dimension of said wave guide appears at multiples of substantially half-wavelengths from said coupling means.
 5. The structure set forth in claim 3 wherein said transition box is substantially two wavelengths square and has its center concentric with said central opening.
 6. The structure set forth in claim 1 wherein said motor means drives said disk at a speed less than 100 rpm.
 7. The structure set forth in claim 1 including: h. a tuning element aligned parallel to said axis of rotation for said disk and disposed in a wall opposite that having said disk adjacent thereto and disposed to produce low microwave power variations for different loads placed in said microwave cavity.
 8. An electronic cooking appliance comprising: a. a microwave generator including coupling means for coupling microwave energy into a wave guide; b. a microwave cavity constructed and arranged to receive objects to be heated and having a central opening formed in one wall thereof; c. a wave guide transition box disposed over said central opening in said cavity, said box and said cavity having walls forming a barrier to the transmission of microwave energy through said central opening, said box having a wave guide opening formed in one wall thereof; d. a wave guide operably connected between said microwave generator and the wave guide opening in said wave guide transition box for conducting microwave energy therebetween; e. a disk rotatably supported about an axis substantially coaxial with said central opening and having a periphery extending outwardly at least to the periphery of said central opening, said disk extending in a plane substantially coplanar with the wall containing said central opening, said disk having a plurality of apertures formed therein with elongated shapes of substantially parallel sides, of which the longer dimension when transverse to the longitudinal dimension of said wave guide appears at multiples of substantially half-wavelengths from said coupling means for distributing said microwave energy between said transition box and said cavity; f. and motor means operably connected to said disk for rotation thereof.
 9. The structure set forth in claim 8 wherein said plurality of apertures have at least two apertures of equal dimensions and at least one aperture of other dimensions.
 10. The structure set forth in claim 8 wherein each of said plurality of apertures has a ratio of length to width of approximately 7.68 to 9.25.
 11. The structure set forth in claim 8 wherein said plurality of apertures are constructed and arranged in said disk so that the longitudinal axes thereof are in non-parallel alignment and the angles between the same are substantially less than normal to each other.
 12. The structure set forth in claim 11 wherein said plurality of apertures are constructed and arranged so that they appear sequentially at multiples of substantially half-wavelengths from said coupling means.
 13. The structure set forth in claim 8 wherein said wave guide has an open end operably connected to the wave guide opening in said wave guide transition box, said wave guide opening extending through a wall substantially parallel to said disk rotational axis.
 14. The structure set forth in claim 8 wherein said disk used with a microwave generator having a frequency of 2450 X 106 Hz has apertures specifically constructed and arranged as shown in FIG. 5 hereof.
 15. The structure set forth in claim 8 wherein said plurality of apertures are disposed in said disk so that the part of said aperture farthest from the center of said disk is less than a wave guide width when transverse to the longitudinal axis of said wave guide.
 16. The structure set forth in claim 1 including: i. a shelf defining a cooking plane disposed below said disk at a distance representative of substantially a multiple of half-wavelengths.
 17. The structure set forth in claim 8 wherein said wave guide transition box includes an indented Ring portion extending downwardly from the top of said box in a smooth curve. 